1. Field of the Invention
The present invention generally relates to a driving circuit and a method thereof, and more particularly, to a driving circuit having dynamically-adjustable output power and high energy efficiency and a method thereof.
2. Description of Related Art
Light emitting diode (LED) has been broadly applied to status indicators on electronic devices, backlight modules of liquid crystal displays, electronic illuminations, automobile lights, traffic lights and signals, flashlights, architectural lightings, or even illumination in projectors for it has such advantages as low electricity consumption and high on/off speed. Moreover, LED has been established in new applications since it was adopted as backlighting of high end cell phones, and the most promising application thereof is to 7-40 inches flat panel displays. The market profit of LED will increase considerably once it is adopted as back lightings of flat panel displays.
When a circuit or backlight module composed of a plurality of LEDs connected in series is driven, the turn-on voltages of the LEDs are slightly different from each other due to process variation, therefore to turn on all the LEDs, the output voltage of the driving circuit is usually set to a high voltage level so as to prevent that a particular LED having higher turn-on voltage cannot be turned on, which causes unnecessary power wastage.
FIG. 1 is a diagram of a conventional driving circuit. The conventional driving circuit includes a boost circuit 100 and a current source unit 140 and is used for driving a plurality of LED strings 111˜119. The boost circuit 100 adjusts the voltage level of the output voltage VOUT according to the duty cycle of the tuning signal SRE. When the driving circuit is in operation, the voltage level of the output voltage VOUT can be determined as long as the input voltage VIN and the duty cycle of the tuning signal SRE are determined, and the output voltage VOUT is adjusted to a high voltage level in order to turn on all the LED strings 111˜119 (to allow them to emit lights). Thus, the current source unit 140 has to receive a lot of voltage drops, and which causes unnecessary power wastage.